柴达木盆地新生代湖相叠层石沉积序列及古环境意义

摘要

Climate,sedimentary environment and lake level are the major factors that intervene the growth of stromatolites directly or indirectly.Correspondingly,stromatolites are certain qualitative indicators for the controlling factors.Comparisons of vertical bedding position and basic sedimentary sequences are made between the two Cenozoic lacustrine stratigraphic sections,Changweitai and Xichagou section in western Qaidam Basin.We identified two Cenozoic high lake-level periods in Qaidam Basin when these stromatolites were thriving,even in adjacent Cenozoic basins in Qinghai-Tibetan Plateau.This might indicate large-scale regional humid climate in Miocene,when strong precipitation and evaporation went simultaneously or alternatively.Four types of basic sedimentary sequences containing stromatolites are proposed,and the stromatolites can develop on the surface of the clay stone or sandstone and conglomerate hard ground.On the top of stromatolitic layer are the fine siliciclastic sediments or sedimentary gap,indicating that the growth of stromatolites follow the minor flooding surface and the sudden rise of relative lake surface.%气候、沉积环境和湖平面的演变直接或间接地影响湖相叠层石的生长,因而叠层石的出现可以作为此三者变化的判别标志.通过对比研究柴达木盆地西部地区西岔沟、长尾台两条新生代陆相地层剖面中近10个湖相叠层石的发育层位、垂向沉积序列,表明叠层石主要发育于新生代两个气候温暖湿润的高湖面时期,而且叠层石沉积亦同时出现在青藏高原其他邻近陆相新生代盆地,显示区域性的大规模异常湿润性气候,以强蒸发和强降水的交替为特征;划分出的4种含叠层石基本沉积序列中,叠层石可在泥岩或砂砾岩硬底上生长,含叠层石灰岩层之上通常是细粒碎屑沉积或间断面,这暗示了叠层石的生长出现在滨湖、浅湖相次级湖泛面附近,或指示湖水的突然加深.